Measurement of changes in intracellular free calcium (Ca2 ion) and intracellular pH in molluscan giant neurons will be continued. Calcium changes will be measured using the metallochromic indicator dye, Arsenazo III; pH will be monitored by phenol red and by pH microelectrodes. Electrophysiological activity will be controlled by voltage clamp and current stimulation. Experiments will be run to investigate internal distribution kinetics of Ca2 ion and H ion following physiological activity. These studies will utilize dye absorbance data in combination with computer modelling studies of Ca and H diffusion in buffering media approximating that of cytoplasm. Direct measurement of the spread of Ca2 ion and H ion in cytoplasm will be made by injection of Ca2 ion and H ion from intracellular micropipettes. The effects of intracellular cAMP and the neurotransmitters dopamine and serotonin on internal (Ca2 ion) and pH will be investigated. We will attempt to correlate changes in electrical activity brought about by these agents with changes in internal levels of Ca and pH.